--- old/src/hotspot/share/runtime/synchronizer.hpp	2020-05-26 17:42:43.000000000 -0400
+++ new/src/hotspot/share/runtime/synchronizer.hpp	2020-05-26 17:42:43.000000000 -0400
@@ -43,11 +43,11 @@
 typedef PaddedEnd<ObjectMonitor, OM_CACHE_LINE_SIZE> PaddedObjectMonitor;
 
 struct DeflateMonitorCounters {
-  int n_in_use;              // currently associated with objects
-  int n_in_circulation;      // extant
-  int n_scavenged;           // reclaimed (global and per-thread)
-  int per_thread_scavenged;  // per-thread scavenge total
-  double per_thread_times;   // per-thread scavenge times
+  volatile int n_in_use;              // currently associated with objects
+  volatile int n_in_circulation;      // extant
+  volatile int n_scavenged;           // reclaimed (global and per-thread)
+  volatile int per_thread_scavenged;  // per-thread scavenge total
+           double per_thread_times;   // per-thread scavenge times
 };
 
 class ObjectSynchronizer : AllStatic {
@@ -132,6 +132,10 @@
   // Basically we deflate all monitors that are not busy.
   // An adaptive profile-based deflation policy could be used if needed
   static void deflate_idle_monitors(DeflateMonitorCounters* counters);
+  static void deflate_idle_monitors_using_JT();
+  static void deflate_global_idle_monitors_using_JT();
+  static void deflate_per_thread_idle_monitors_using_JT(JavaThread* target);
+  static void deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* target);
   static void deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters);
   static void prepare_deflate_idle_monitors(DeflateMonitorCounters* counters);
   static void finish_deflate_idle_monitors(DeflateMonitorCounters* counters);
@@ -141,10 +145,26 @@
                                   int* count_p,
                                   ObjectMonitor** free_head_p,
                                   ObjectMonitor** free_tail_p);
+  // For a given in-use monitor list: global or per-thread, deflate idle
+  // monitors using a JavaThread.
+  static int deflate_monitor_list_using_JT(ObjectMonitor** list_p,
+                                           int* count_p,
+                                           ObjectMonitor** free_head_p,
+                                           ObjectMonitor** free_tail_p,
+                                           ObjectMonitor** saved_mid_in_use_p);
   static bool deflate_monitor(ObjectMonitor* mid, oop obj,
                               ObjectMonitor** free_head_p,
                               ObjectMonitor** free_tail_p);
-  static bool is_cleanup_needed();
+  static bool deflate_monitor_using_JT(ObjectMonitor* mid,
+                                       ObjectMonitor** free_head_p,
+                                       ObjectMonitor** free_tail_p);
+  static bool is_async_deflation_needed();
+  static bool is_safepoint_deflation_needed();
+  static bool is_async_deflation_requested() { return _is_async_deflation_requested; }
+  static bool is_special_deflation_requested() { return _is_special_deflation_requested; }
+  static void set_is_async_deflation_requested(bool new_value) { _is_async_deflation_requested = new_value; }
+  static void set_is_special_deflation_requested(bool new_value) { _is_special_deflation_requested = new_value; }
+  static jlong time_since_last_async_deflation_ms();
   static void oops_do(OopClosure* f);
   // Process oops in thread local used monitors
   static void thread_local_used_oops_do(Thread* thread, OopClosure* f);
@@ -155,6 +175,8 @@
                              outputStream * out, int *error_cnt_p);
   static void chk_global_free_list_and_count(outputStream * out,
                                              int *error_cnt_p);
+  static void chk_global_wait_list_and_count(outputStream * out,
+                                             int *error_cnt_p);
   static void chk_global_in_use_list_and_count(outputStream * out,
                                                int *error_cnt_p);
   static void chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
@@ -169,12 +191,17 @@
   static int  log_monitor_list_counts(outputStream * out);
   static int  verify_objmon_isinpool(ObjectMonitor *addr) PRODUCT_RETURN0;
 
+  static void do_safepoint_work(DeflateMonitorCounters* counters);
+
  private:
   friend class SynchronizerTest;
 
   enum { _BLOCKSIZE = 128 };
   // global list of blocks of monitors
   static PaddedObjectMonitor* g_block_list;
+  static volatile bool _is_async_deflation_requested;
+  static volatile bool _is_special_deflation_requested;
+  static jlong         _last_async_deflation_time_ns;
 
   // Function to prepend new blocks to the appropriate lists:
   static void prepend_block_to_lists(PaddedObjectMonitor* new_blk);